Stimulating the nasal cavity exerts a powerful and abrupt alteration of respiratory and cardiovascular rhythms. This remarkable behavior is present in all vertebrates, including man, and commonly is called the diving reflex. The control is mediated through the central nervous system, which possesses the neuronal circuits directing cardiorespiratory function. However, no information is available regarding the specific central neural circuits driving this behavior. My long-term objective is to establish the brainstem reflex pathways utilized in the diving reflex in mammals. The general aim of this proposal is to establish the trigeminal component of these circuits; it specifically aims to 1) determine the locus within the trigeminal sensory complex which receives sensory fibers from the nose and upper respiratory passages using transganglionic transport methods; 2) validate the importance of this area as the trigeminal mediator of cardiorespiratory function using both reversible blocking agents (lidocaine and muscimol) and electrical and chemical (glutamate) stimulation; 3) determine the projections of neurons in this area to brainstem autonomic nuclei using conventional neuroanatomical techniques (HRP, PHA-L, tritiated amino acids); 4) specifically determine the role of the trigeminoparabrachial pathway in the response using blocking agents and if this pathway uses opiates as a chemical messenger (double labeling techniques and naloxone injections). The powerful inhibition of respiration and heart resulting from upper respiratory stimulation may provide a neurogenic basis for the tragedy of the Sudden Infant Death Syndrome (SIDS) and the cardiorespiratory alterations seen in simple intubation procedures. Understanding the brainstem circuitry of the diving response could aid in the diagnosis and remedy of these problems. Knowledge of these same brainstem circuits will serve as a substrate for future investigations of how a simple somatic stimulus could be designed to modulate autonomic behavior and how higher levels of the brain (i.e. limbic) influence cardiorespiratory activity usually controlled at lower levels.